Progressive cognitive impairment occurs in up to 50% of primary and metastatic brain tumor patients who survive 6 months or longer after treatment with partial or whole-brain irradiation (WBI); ~200,000 patients/year receive these treatments. A growing body of evidence suggests that oxidative stress and pro-inflammatory responses play a critical role in radiation-induced brain injury. These observations provide the rationale for investigating anti-inflammatory-based therapeutic approaches to ameliorate or prevent radiation-induced brain injury. This competitive renewal will focus on the role of the peroxisomal proliferator-activated receptors and (PPAR, PPAR) in ameliorating or preventing radiation-induced brain injury, including cognitive impairment. These PPARs are potent mediators of anti-inflammatory responses. During the current funding period, we have demonstrated that i) administration of the PPAR agonist, pioglitazone, prevents fractionated WBI- induced cognitive impairment in young adult male rats; ii) the irradiated brains of PPAR KO mice have increased microglial activation, iii] administration of the PPAR agonist, fenofibrate, prevents both WB-induced microglial activation and decreased neurogenesis, and iii) pre-treatment of microglial cells with PPAR agonists prevents radiation-induced increases in inflammation. In this competitive renewal, we propose to extend our PPAR studies and initiate studies on PPAR, increasingly recognized as a promising pharmacological target for neuroprotection. We hypothesize that administration of PPAR and/or PPAR agonists will not only ameliorate or prevent radiation-induced brain injury, including cognitive impairment, but will also inhibit brain tumor growth. To test this hypothesis, we will pursue the following Specific Aims: 1] using a fractionated WBI rat model, we will determine if administration of PPAR or PPAR agonists will ameliorate or prevent radiation-induced brain injury, including cognitive impairment; 2] using PPAR KO mice, we will determine if i] knocking down PPAR will increase radiation-induced brain injury, and ii] if administering a PPAR agonist will ameliorate or prevent radiation-induced brain injury through PPAR- dependent mechanisms; 3] using murine hippocampal neurons and microglial cells, we will determine if incubating these cells with PPAR agonists modulates radiation-induced changes in cellular phenotype via inhibition of pro-inflammatory signaling pathways and/or upregulation of anti-inflammatory mediators; and 4] using human glioma cell lines and immortalized normal glial cells, we will determine if treating with PPAR or PPAR agonists leads to selective glioma cell kill. Further, we will use an in vivo orthotopic rat model to determine if administering PPAR or PPAR agonists, alone or in combination with ionizing radiation, inhibits tumor growth and increases survival times. Successful completion of these aims will serve as the foundation for translating these findings into clinical trials designed to enhance the quality of life and long-term survival of cancer patients receiving partial or WBI. .